Organic compound and method of treating the same



252. COMPOSITIONS, I .1

Patented Aug. 8, 1933 UNITED STATES PATENT OFFICE James H. Gravel], Elkins Park, Pa.

No Drawing.

Application May 15, 1931 Serial No. 537,758

3Claims.

This invention relates to the art of metal pickling and is more particularly directed to metal pickling baths for pickling steel.

The objects of the invention are to provide a selectively controlled metal pickling bath employing any one of an enlarged list of available selective controlling materials, not generally available today for this purpose.

More specifically the invention consists in reducing the body of the selective controlling material to very fine particles, of a size such that they will remain suspended throughout the pickling bath, by the natural circulation of the bath and in producing an excess of such material so that there will remain in the bath undissolved suspended material available for limiting the action of the acid on the metal in all partsof the bath at all times.

It has been my experience heretofore that a relatively limited number of materials can be satisfactorily employed for selectively controlling pickling baths mainly because the particles are not available adjacent the work being pickled for controlling the action of the acid. This probably results from the fact that in the pickling act the acid dissolves the particles of the controlling material which are adjacent the metal for controlling the action of the acid and none or not a sufiicient number are left over from the saturated solution to exist as floating particles to perform the intended inhibiting action. Where the selective control material is not divided into extremely fine particles and supplied in quantity in excess of that required for saturation additional particles of the control material are not available for dissolving in the acid bath adjacent the work to take the place of the particles so dissolved and to furnish an excess amount for suspension in the bath, hence the action of the acid is substantially uncontrolled.

There are two satisfactory methods of mechanically dividing the control material into particles of the desired fineness, these methods being as follows:

First, the proper degree or fineness may be obtained by dissolving the water insoluble material in a suitable solvent and then adding the solution in sumcient amount to the admixture of water and acid, used to cause saturation of the bath and an excess amount which is precipitated as undissolved material in extremely fine particles in the pickling bath. The finely divided excess material thus produced will exist as floating particles which will not be dissolved by the solvent of the bath and which will be suspended therein by the material circulation thereof and operate as the active inhibiting material. Such solvents as alcohols, keytones, esters, ethers. strong concentrated sulphuric acid and those solvents which will dissolve the controlling agent and which are soluble in water, are suitable for my purpose provided they are substantially anhydrous and sufliciently concentrated.

Second, satisfactory results may be obtained by grinding the selective control material into very fine particles in an ordinary mill and screening the product discharged from the mill so that only very minute particles of the material are obtained. Such grinding machines or mills are known commercially and hence will not be described in detail.

Any other means may be adopted whereby the selective controlling substance will be supplied in quantity to remain suspended in a metal pickling bath without departing from my broad invention.

I have found that many organic compounds containing sulphur and nitrogen, such as are found in that class of material known as rubber accelerators, which in themselves exhibit either very weak control properties or no control properties at all, when tested by methods heretofore applied, show strong selective control properties when applied according to my invention. For example, anhydroformaldehydeaniline, thiocarbanilide, dio'rfthotolylthiourea, etc., show very "weak'control properties or no such properties at all when used in their commercial form but when used according to my invention produce effective and satisfactory results. It is accordingly an object of the present invention to enlarge the list of available metal pickling control substances by making available a large number of substances which are substantially insoluble in metal pickling baths after the bath has been saturated therewith, but which may be employed effectively when they are sufficiently finely divided by any known means and used in excess quantity to provide active particles suspended in the bath.

To prepare a commercial bath for pickling steel, I may use for example,

Water 10,000.00 gallons Sulphuric acid (66) 500.00 gallons Diorthotolylthiourea 1.00 pound more or less according to the amount of selective controlling material desired in the bath in a finely divided floating condition and according to the rapidity of the action desired.

Examin The diorthotolylthiourea in suflicient amount may be dissolved in strong sulphuric acid and the admixture added to the water while stirring, or the water and a portion of the acid may be admixed and the diorthotolylthiourea dissolved in the remainder of the acid and then this admixture containing the diorthotolylthiourea is added to the aqueous bath, the acid dissolves in the water and causes the diorthotolylthiourea to precipitate in particles of suflicient fineness to remain suspended mechanically in the pickling bath and, due to the currents naturally present when pickling, to be difiused throughout the bath and to act as a powerful selective controlling agent.

Similar results may be obtained by grinding up the selective control material and sitting out only the very finely divided powder which is then added to the acid bath in substantially the following proportions:

Finely divided diorthotolylthiourea- 1.00 pound Water 10,000.00 gallons Sulphuric acid (66) 500.00 gallons It is found that the grinding of the material into the relatively fine powder has a similar effect to dissolving the material in a strong acid up to saturation point and permitting the excess material to precipitate in the bath.

Many selective controlling materials which are substantially valueless, from a commercial standpoint, if added directly to the bath, may be of great commercial value if the bath is prepared according to the present invention. For example, if commercial diorthotolylthiourea is directly added to the pickling bath its efiect is relatively very weak, due probably to the fact that the amount of the material adjacent the work is very soon exhausted from the bath and none remains available for continuing the control of the bath, but when used according to my invention its efiect is very powerful. The above statements have been established by actual tests. If a pickling bath be prepared as described above with diorthotolylthiourea omitted and heated to about 180 F., it may be used continuously for pickling steel for about thirty minutes, at which time the acid becomes exhausted. If commercial diorthotolylthiourea be added to the same bath the time before the bath exhausts itself is not materially longer. It may be perhaps thirty-five minutes. If, however, the diorthotolylthiourea be added according to my invention in quantity to provide active particles floating in suspension the bath will last much longer or approximately eighty minutes before becoming exhausted.

Owing to the very fine division of the particles of material for selectively controlling the bath, as set forth in the present application, the particles of the substance are, practically speaking, not subject to the effect of gravity. Hence, the particles of control material float around and remain suspended in the bath without being actually dissolved therein and without the necessity for any type of buoying agent.

What I claim is:

1. The method of preparing a metal pickling bath comprising a pickling acid and water with a regulator for selectively controlling the action thereof, which consists in dissolving in an acid solution of greater strength than the bath a predetermined quantity of a selective solid control material which is insoluble in water and soluble weakly in the acid bath the amount of material being in excess of that capable of being dissolved by the bath strengthened by the addition of the solution thereto, adding the solution to the relatively weak acid bath so as to efl'ect the absorption by the bath of the acid of the solution, and causing by the differential solvent capacity between the normal and strengthened bath the precipitation of the excess of control material in the bath in the form of finely divided dispersed particles having the property of floating in the bath and remaining suspended therein by the action of the natural circulation of the bath,

2. The method of preparing a metal pickling bath embodying a pickling acid and water with a regulator for selectively controlling the pickling action of the bath, which consists in dissolving diorthotolylthiourea in a strong solvent, and adding the solution to the bath so as to effect the absorption of the solvent thereby and the precipitation of the diorthotolylthiourea in the form of finely divided floating particles throughout the bath.

3. The method of preparing a metal pickling bath embodying acid and water with a control agent which comprises dissolving a thiourea body in a strong solvent, and adding the solution to the bath so as to efiect the absorption of the solvent thereby and the precipitation of a proportion of the thiourea in the form of finely divided particles dispersed throughout and floating in suspension in the bath under the natural circulation thereof.

JAMES H. GRAVELL. 

